normally the pushback procedure occurs when the aircraft is fuelled and passengers have embarked
As mentioned in previous post, if the aircraft is being re-positioned but normally towing would achieve this unless at a remote airfield with next to no ground equipment available.
pushback begins roughly at the same time as engine start
Pushback starts once brakes have been released and then engines are started when the headset man has given the pilot clearance to do so.
Occasionally the engine(s) are started prior to pushback, if the APU or APU bleed has failed and air start trucks are then used on the bay.
Pax would be onboard before start as doors are closed prior to engines starting and taxi-ing in your example.
start procedures begin?
Do I detect this as to be 'starting engine procedure' or 'starting cockpit procedure', hence why you ask whether pax have embarked...??
1/ Generally
2/ Don't know
3/ Towing from a remote parking bay
4/ Ground electrical power would possibly show messages or indications only as no air source available.
With the APU running and air bleed selected then you will be advised of a bleed fault if and when it occurs.
With the aircraft COLD and DARK you will not know of any faults unless it was written in the Tech Log on the previous arrival.
Some thoughts for you to discus further...
TW